(a) Technical Field
The present invention relates to a multi-stage in-line cartridge ejector. More particularly, the present invention relates to a multi-stage in-line cartridge ejector for a fuel cell system, which serves as a hydrogen recirculation blower of a fuel processing system in a fuel cell system to increase the amount of recirculated hydrogen, thus improving the system performance.
(b) Background Art
In general, a fuel cell is capable of producing a direct current by converting chemical energy of a fuel gas directly into electrical energy. Unlike other conventional batteries, the fuel cell generates electricity continuously by utilizing fuel and air supplied from the outside.
Hydrogen used as a fuel in the fuel cell may be pure hydrogen or reformed hydrogen generated by a reforming process using a hydrocarbon such as methane or ethanol.
Recently, the fuel cells have been applied to vehicles, and extensive research and development aimed at development of fuel cell vehicles have continued to progress. Such fuel cell vehicles have the same characteristics as electric vehicles and there is no fundamental difference, except that the fuel cell vehicles are more environment-friendly and can use pure hydrogen or reformed hydrogen as an energy source to generate electrical energy.
In a fuel cell system using hydrogen as a fuel, hydrogen is supplied from a hydrogen tank to a fuel cell stack and the amount of hydrogen gas supplied to the fuel cell stack is controlled by a controller. Meanwhile, air used in the fuel cell is supplied to the fuel cell stack through a compressor.
Usually, the air and hydrogen are supplied to the fuel cell in an amount larger than the amount required for electrochemical reaction in order to ensure a certain level of the performance of the fuel cell stack and increase the lifespan thereof.
Unreacted hydrogen remaining in the fuel cell stack is recirculated to prevent waste of fuel, thus increasing the overall efficiency of the system.
Especially, the technique for recirculating the unreacted hydrogen is crucial to improve fuel efficiency of the fuel cell system. A blower means has been typically used to recirculate the unreacted hydrogen discharged from the fuel cell stack to a stack inlet.
Since conventional blower means has several drawbacks in that it has a complex structure, requires lubrication, and causes noise and vibration, techniques to recirculate the unreacted hydrogen using an ejector means have been proposed.
The ejector means for hydrogen recirculation has advantages in that it has a simpler structure than that of the blower means, it does not require lubrication since rotational elements are not used therein, and it does not cause noise and vibration; however, there is also a problem in that the ejector means has a narrow operation range and thus it is not suitable to apply it to the fuel cell vehicle in which the load is rapidly changed.
In order to solve such drawbacks, there have been various approaches to widen the operation range of the ejector means. One approach was to use a plurality of ejectors to increase the operation range, as proposed by some Japanese vehicle manufacturers.
However, this approach has some drawbacks in that the plurality of ejectors occupy much space in a vehicle, manufacturing costs increase due to increased number of parts, flux control of the ejectors is not sufficiently accurate due to the difficulty in manipulation of a hydraulically driven needle used therein.
Further, the approach is disadvantageous in that since two or three ejectors are interchanged or switched additional elements such as a device for interchanging or switching the ejectors and a device for preventing reverse flow, thereby inviting a complexity of the structure.
As another example of the ejector means, there is a variable nozzle type ejector in which the position of a needle is controlled by an electric motor means to adjust the pressure and amount of hydrogen gas. However, it has several drawbacks in that it is expensive and it encounters a pressure loss or leakage problem.
The information disclosed in the Background section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.